Even
a well-rested crew cannot reasonably be expected to helm the boat for
more than two four-hour shifts a day. That means it takes three crew to
continuously helm a boat like Jocara. In our minds, then, a good autopilot
is worth three crew, plus it never gets tired or falls asleep at the wheel
and doesn't need a place to sleep or be fed!

As
with all critical items on board, there must be backups. In the past,
we've had an electronic autopilot and a purely mechanical backup - which
makes sense since it could replace the electronic autopilot in the event
of autopilot failure or electrical power failure. Jocara, however, is
a heavy boat and, particularly for downwind sailing, difficult to manage
with a mechnical system. Besides, we have enough stuff cluttering the
stern already (see the davits
section)!

We
therefore have two (almost identical) electronic autopilots on board,
made by Cetrek in the UK. They each consist of a central computing unit
with an electronic fluxgate compass and rudder position indicator as input
devices and a hydraulic pump that drives the steering rams as output.
The system human interface is through a control head in the cockpit.

The
computer senses the direction of the boat and commands the rudder pump
to produce corrective rudder movements, sensing the response of the rudder
and the induced yaw of the vessel as feedback to tune its responses. Because
it knows how much rudder has actually been applied, and the boats response,
in addition to the 'noise' in the ship's heading caused by the waves,
the unit can assess the sea state and adapt its control accordingly. As
a result, when it works, it generally does a better job than a human helmsman!

The
main autopilot computer. A temperature gauge can be seen to the
left. It relays the compartment temperature to a display at the
navigation station.

One
of the Cetrek autopilot 'heads'. This is the portable one, very
useful for leaning out over the rail to see shallows and being
able to con the boat at the same time!

We
have two independent systems, the only difference between them being the
control head, one of which is a portable hand-held unit on a coiled line,
the other fixed in the instrument bulkhead. Their functionality is identical.

We've
had trouble with them losing calibration, and with the HF radio scrambling
the communications to the control head while they are operating, so that
they switch off or become confused during radio transmissions. We also
find that the generator, placed in the same compartment as the computers
and compasses, understandably affects the compasses when operating.

A
fluxgate compass, mounted on the athwartships bulkhead at the
forward end of the compartment under the cockpit. No metal or
magnetic materials allowed in this area! Unfortunately, it is
close to the 140-amp alternator on the generator...

The
two hydraulic pumps, one for each separate autopilot system. One
of the Cetrek computer casings can be seen on the left-hand side.